The present invention relates to a support element for an extracorporeal fluid transport line, and to an extracorporeal fluid transport line, particularly for infusion devices for medical use.
In particular, the support element and the line according to the invention are used in apparatuses for the extracorporeal treatment of blood, for example apparatuses for dialysis and/or plasmapheresis, in order to provide an infusion line which can be connected to an extracorporeal blood circuit associated with the aforementioned apparatuses; the support element and the line in question can also be used for forming an infusion line which can be connected directly to the patient's vascular system.
As is known, a conventional infusion line comprises at least one length of tubing designed to connect a bag containing a specified infusion liquid to an extracorporeal blood circuit or directly to a patient through conventional access means such as needles, catheters or the like. For example, U.S. Pat. No. 5,698,090 in the name of Hospal Industrie describes an infusion line comprising a bag containing a replacement liquid; the infusion line leads to a collection chamber (or bubble trap) in which the infusion liquid can be combined with the blood obtained from a venous branch of an extracorporeal blood circuit.
The collection chamber enables a liquid-air separation process to be conducted, thus preventing the propagation of dangerous gas particles towards the patient. The separated gas can be discharged directly to the exterior, or suitably handled by means of a pneumatic circuit connected to the top of the collection chamber. Downstream of the aforesaid chamber, the blood, having been enriched with the infusion liquid, is returned to the patient's cardiovascular system.
It is clear from the above description that the collection chamber must always contain a specified minimum volume of liquid if it is to function properly; otherwise, if no liquid level were formed in the collection chamber, there would be a risk of transferring gas directly to the patient.
Furthermore, the dimensions of the collection chamber must be such that the blood flow is slowed so that there is time for the gas particles to be separated by moving towards the top of the bubble trap.
In practice, the collection chamber has a radial dimension considerably greater than that of the infusion tube. Consequently, where the manufacture of the line is concerned, the collection chamber must be made in more than one piece and is typically made separately from the rest of the line. The various lengths of tubing forming the infusion line and the various parts of the collection chamber are then assembled by a process which adds to the total cost of the infusion line.
Furthermore, the devices which have been described typically require the presence of level sensors and/or air bubble sensors interacting, by means of a control unit, with at least one safety valve, for example a clamp, which can close the tubing as soon as a critical condition is detected in the bubble trap. Clearly, the fluid collection chamber can separate air from the liquid only when a minimum quantity of liquid is present in the chamber: if the liquid in the collection chamber is used up (this inevitably occurs after a certain time when the infusion liquid has been used up, unless the infusion pump is stopped at the correct time), there will be a transfer of gas towards the patient.
Infusion lines with bubble traps also have some critical aspects in relation to their use: both the tubes and the collection chamber are normally fixed to a face panel, of a blood treatment apparatus for example, or in any case are fixed to a suitable support and positioning system; in particular, the collection chamber must be fixed in a precise way, especially when it interacts with level and/or air bubble sensors. In terms of operation, a significant length of time is therefore required to enable the line to be prepared correctly for use.
Finally, because of their structure, lines with collection chambers are poorly adapted to installation in small spaces.
For the sake of completeness, it should also be mentioned that there is a known air-liquid separator comprising a containing body forming two adjacent chambers separated by a hydrophilic membrane; the containing body has an inlet aperture for a fluid comprising liquid and gas particles. The liquid can pass through the hydrophilic membrane and emerge through an outlet aperture. The gas which reaches the first chamber is discharged through secondary apertures positioned upstream of the hydrophilic membrane, at least one hydrophobic membrane being used at these apertures to prevent the liquid from passing through.
The device which has been described allows the fluid, containing gas particles, to be separated into two parts, namely a liquid phase which emerges from the outlet aperture provided in the second chamber, and a gas phase which is released through the secondary apertures provided in the first chamber. It should be noted that the air separator device which has been described does not require a constant presence of liquid stagnating within it in order to separate the gas; in other words, the fluid passing through the separation device is continuously divided into the liquid, which continues along the line, and the gas, which is discharged to the exterior.